Fix JavaScript TypeError: X is not a constructor (2025 Guide)

Fix TypeError: X is not a constructor in JavaScript - 2025 Guide

Posted on: March 20, 2025

Seeing a "TypeError: X is not a constructor" in JavaScript? It means you tried to use something as a constructor that isn’t one. Let’s fix it fast in this 2025 guide!

What Causes "TypeError: X is not a constructor"?

This error occurs when you try to use the new keyword on something that isn’t a constructor. Common causes:

• Not a Class/Function: Using new on a non-function value.
• Import Issues: Incorrectly importing a module.
• Typo: Misspelling the constructor name.

Check this demo (open console with F12):

Here, NotAClass is a regular function that doesn’t support new, causing the error.

How to Fix It: 3 Solutions

Let’s resolve this error with practical steps:

(Diagram: Developer uses new, gets error, fixes constructor, creates instance.)

Solution 1: Use a Proper Constructor

Ensure you’re using a class or constructor function:

// Wrong
function NotAClass() {
  return "Not a class!";
}
const instance1 = new NotAClass();

// Fixed
class MyClass {
  constructor() {
    this.name = "MyClass";
  }
}
const instance2 = new MyClass();
console.log(instance2);

Use class or a proper constructor function with new.

Solution 2: Fix Import Issues

Check how you’re importing modules:

// Wrong (assuming ES modules)
import myFunc from './myFunc'; // myFunc is not a constructor
const instance = new myFunc();

// Fixed
import MyClass from './MyClass'; // MyClass is a constructor
const instance = new MyClass();
console.log(instance);

Ensure the imported module is a constructor.

Solution 3: Fix Typos

Double-check constructor names:

// Wrong
class myClass {
  constructor() {
    this.name = "myClass";
  }
}
const instance = new Myclass(); // Case mismatch

// Fixed
class MyClass {
  constructor() {
    this.name = "MyClass";
  }
}
const instance = new MyClass();
console.log(instance);

Match the case and spelling of constructor names.

Quick Checklist

• Is it a constructor? (Use a class/function)
• Is the import correct? (Check module)
• Any typos? (Verify names)

Conclusion

A "TypeError: X is not a constructor" can break your code, but with these 2025 solutions, you’ll instantiate objects correctly. Got another JavaScript error to fix? Let us know in the comments!